Water Scorpion Care and Habits – Aquatic Insects for Arachnid Fans

Over the past several months, I’ve spent much time collecting aquatic insects with my nephew, who is quite the intense little naturalist (please see photos – I’m having as much fun as he!). In addition to our usual haul of backswimmers, predacious diving beetles, dragonfly larvae and the like, this season I was pleased to find a healthy population of Brown Water Scorpions (Ranatra fusca). Combining characteristics of mantids, walking sticks and scorpions, all modified for life underwater, these amazing creatures are simple to keep and fascinating to get to know.

Aquatic Insects as Pets

In years past, I set up aquatic insect exhibits for several zoos and public aquariums, but it seems that interest remains rather low among private invertebrate keepers. This surprises me, as their range of lifestyles rivals that of their land-bound cousins, and never fails to astonish me even after all these years. Please see this article for information on aquatic beetle care, and watch for others in the future.

Natural History

Classification

Water Scorpions are classified in the order Hemiptera and the family Nepidae. Members of the order Hemiptera, known as True Bugs, have sucking, beak-like mouthparts. Examples include cicadas, giant water bugs, backswimmers, leafhoppers and aphids. Approximately 270 Water Scorpion species have been described worldwide, 13-15 of which inhabit North America. No doubt many others are awaiting “discovery”.

Physical Description

The body of the Brown Water Scorpion resembles that of a terrestrial stick insect and is yellowish-tan to dark brown in color. Others, including those in the North American genus Nepa, are flattened in appearance. The front legs are raptorial (designed for grasping) and superficially similar to those of a praying mantis. Unlike a mantis, however, the terminal segments of the Water Scorpion’s front legs fit into a groove when not in use, and swing out like folding knives when needed. These hook-like leg tips can be seen in the photo showing a Water Scorpion poised just below a guppy.

The middle and hind legs are about as long as the body, and paired breathing tubes are situated at the end of the abdomen. This species reaches 1.75 inches in length (to approximately 3 inches including the breathing tube).

Water Scorpions can fly, but do so only rarely.

Amazing Organs

Three pairs of disc-shaped organs on the abdomen, known as false spiracles, enable Water Scorpions to gauge water depth and compensate for changes in water pressure.

Range

From southern Canada through much of the continental USA to northern Mexico.

Habitat

Poorly adapted for swimming, Water Scorpions favor the still waters of ponds, swamps, lake edges and canals, where they remain immobile among plants and sticks. The photo of my nephew “waiting in ambush” shows their typical habitat.

Diet

This voracious carnivore feeds largely upon the body fluids of invertebrates, but will also take small tadpoles, fishes and newts. Water Scorpions are ambush predators, relying upon camouflage when hunting. They lash out with the front legs and subdue prey via salivary fluids injected through the sharp beak. These fluids contain chemicals that tranquilize prey and initiate digestion; food is consumed in liquid form, in the manner of spiders.

Reproduction

Eggs are inserted into living or dead plants, and hatch in 2-4 weeks. The nymphs resemble the adults (incomplete metamorphosis) and mature in 4-6 weeks.

Captive Care

Enclosure

The aquarium should be covered and the water slow-moving. Water Scorpions are poorly-equipped for swimming, and will perish if buffeted by strong currents.

The tank should be well-stocked with plants (preferably live) and sticks that rise to the water’s surface. Water Scorpions breathe by extending the abdominal breathing tubes above the water’s surface, and cannot utilize oxygen dissolved in the water. They will not thrive if unable to station themselves on a plant or stick near the water’s surface.

Filtration and Water Quality

Water Scorpions may be kept in an unfiltered bowl, jar, or aquarium if provided a weekly water change (please see photo of my simple enclosure). Live plants will enhance the aquarium’s appearance and assist in maintaining water quality. If filtration is desired, be sure to avoid strong water currents. Sponge, undergravel, and corner filters are ideal.

Although Water Scorpions inhabit waters that are often subjected to varying pH and ammonia levels, water quality should not be ignored. In this regard, they should be maintained as are tropical fishes (please write in if you need further information). Water used in the aquarium should be treated with chlorine/chloramine removal drops and maintained at pH 6.8-7.2.

Light, Heat and Water Quality

Temperatures of 65-82 F are well-tolerated.

Feeding

Water Scorpions are attracted to prey by movement, and will take small crickets and bits of fish, shrimp and earthworm from tongs. I also offer small guppies, mosquito larvae and blackworms. I’ve not seen them take smaller prey items, but mosquito larvae do disappear (and seem not to be buzzing about the house!).

Compatible Species

In common with many aquatic insects, Water Scorpions will consume smaller individuals of their own species. However, as captive breeding seems not to have been recorded, keeping several in a well-planted aquarium would be worthwhile (reduced temperatures and a shortened light cycle in winter may encourage reproduction).

These slow, deliberate hunters will not get enough food in aquariums housing diving beetles, water boatmen, fishes and other aggressive feeders. In such situations, they must be individually fed via tongs.

Captive Longevity

Adults over-winter and can live for 2 – 2.5 years.

Handling

As you can see from my 4-year-old nephew’s smiling face, Water Scorpions are rather “stiff” and cannot bite if held as illustrated. The long beak seems quite formidable, but several observers report that it cannot pierce human skin (this re Brown Water Scorpions; others not mentioned). I’m wary of aquatic insects, however, as even the smallest predatory species can usually inflict a painful bite. After so many decades of being bitten and stung by creatures large and small, I have no desire to experiment! I advise that you handle via tongs or a net.

What Can I Do?

Insects and other invertebrates occupy every conceivable aquatic habitat, from birdbaths to swamps and even the sea. Running a net or small strainer through just about any bit of available water will yield a treasure trove of interesting creatures, many of which are quite easy to keep and even breed. So get out there and look around, and please feel free to write in with suggested topics, so that I can cover your favorite species.

15 comments

i have been looking for a page like this for a week. i have a full grown Ranatra that i caught in a pond in my back yard about a week ago and recently added a second adult yesterday. i am currently keeping them in a small 2 gallon aquarium along with a few small crayfish and mud minnows, 2 ghost shrimp and a dragonfly nymph that should hatch and fly soon and they all get along quite well. i have watched the Ranatra eat other insects as small as Daphnia (aka water fleas), their favorite food seems to be mosquito larvae which they snatch up faster than anything else. i was actually surprised this morning to find out that the second Ranatra i add to my tank yesterday was a female since what i originally thought to be fighting turned out to be mating on closer inspection. as far as i can tell they are relatively easy to breed as long as you have both sexes, males are slightly smaller that the females. any questions about the Ranatra are welcome and i will answer as best i can.

will do. it was honestly a stroke of luck that they bred but from what little I’ve read and seen so far they breed from spring to early summer, i feed them about 2-3 times a day so there is a constant food supply available, i also change the water every 2-4 days to keep it clear and algae free. il watch the plants in the tank closely for eggs and take pictures of any i find.

Thanks, Clayton, very interesting. Food seems to be the key in keeping most aquatic bugs…I’m trying to breed giant water bugs right now; they are ravenous, eat minnows regularly, but start on each other when without food for even a short period of time; good luck, enjoy, Frank

im not a fan of the Giant Water Beetle myself, they are an interesting bug but yes they are probly the only bug able to out hunt a mature dragonfly nymph. i however had some recent difficulties with the Ranatra, my male seems to have “disappeared” due to the “Dragonfly nymph factor”. i moved my female it a gallon jar by herself but i might have to wait till next year to attempt breeding again. im still hopeful tho.

Hi Frank,
i work for a children’s museum and i have been wanting to set up a tank with aquatic insects in it in our ‘bug’ exhibit area for a while. i finally got the tank all set up and then went out bug hunting and really couldnt find much. (i got excited and didnt check before i started my project.) i think it has been too hot and dry lately. do you have any recommendations of places where i could order online some cool looking aquatic insects? (i will keep hunting around in the meantime!)
also, one of the few types of insects i managed to catch is the Gerridae (water skeeter). what would you recommend i feed them?
thanks!
louise

They’ll take fruit flies and pinheads, also crushed bits of larger insects. Most species will accept floating tropical fish flakes as well. A bit delicate spometimes…if they get splashed etc while you are working in tank, they do not always seem to dry off well and recover. but lots of fun.

I have best luck by dragging a flat-bottomed net (gen sold by fish hatcheries, etc) through heavy cover; a minnow trap baited with raw fish will nab water scavenger beetles, predacious diving beetles if they are about.

Hi Frank,
i just found a reference to Hatari or bugs of America LLC on one of your other pages. would you say that i could have both whirligig beetles and water scorpions together if i target feed the scorpion as you said above?
thanks again!
louise

Sorry for the delay; great that you are using aquatics…I had great reactions to exhibits I set up at the Brooklyn Children’s Museum, Bx Zoo and Maritime Aquarium. Think also about water scavenger beetles, diving beetles, as very active. giant water bugs very impressive, dragonfly larvae always eager to feed, let me know if you need other ideas, care info.

Call Barney Tomberlain, owner of Hatari…best in the business. Availability fluctuates, and list isn’t always up to date…but tell him what you are looking for and he’ll let you know when to expect them, will have other ideas usually as well. He’s a gem; tell him you were referred by Frank Indiviglio, Bronx Zoo. I’m trying to breed some giant water bugs he sent me in the spring. What museum are you at?

You can keep water scorps with whirligigs if you feed as mentioned…cover well, whirligigs often fly at night, squeeze through tiny openings,

Hi Frank!
I found your pet blog while searching for information on a water scorpion I accidentally collected while scooping algae for my pet pond snails and daphnia.
I decided to see if it were possible to rear this guy since he is so neat!

I have a few questions about it if you wouldn’t mind helping me?
1. I have no other predators and only a small jar (4-5L, with daphina, pond snails and algae in it. I could adapt the tank to suit my new friend, or I could keep him separate. I have a, 8L jar that I could grow more algae in. Any suggestions either way?

2. I was going to try to feed him/her an earth worm and then things I find close to ensure a continuous supply. Do you think an investment into crickets or brine shrimp would be a better/more consistent idea?

3. Most importantly how often do I need to feed him/her (times per day)?

I’m very excited, and I am so happy to hear some one else appreciates various freshwater invertebrates as much as I!

You can keep it in current jar or new…they may grab at snails and larger Dahnia, but most likely would not. Provide a stick for it to cling to.

Small earthworms fine, blackworms (sold for tropical fish); brine shrimp might be taken if lg enough, but no need to but; any small insects, bits of fish meat from tongs also taken; mosquito larvae also relished.

They can gear metabolism to food availability..ideal pets, can fed near-daily to once weekly! Much depends on temperature and meal size, but very adaptable.

If you are in the USA, all species can be cared for as described in this article. Asian species may be similar, but could also have very different habits and needs,…you’d need to accurately identify the species to be sure. best not to handle any that you cannot identify…they bite, which can be very painful, and there’s always the chance of an allergic reaction to their venom. Best, Frank

About Frank Indiviglio

Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.

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